1. Field of the Invention
The present invention relates to a non-interlace display device to be applied to an image display device of large scale where, for example, a number of display elements are arranged in two-dimensional manner.
2. Description of the Prior Art
For example, an image display device of large scale has been developed where a number of display elements are arranged in two-dimensional manner as disclosed in Japanese patent application laid-open No. 177078/1986.
Also in such an image display device, a scan line conversion device during indicating so-called high vision signals has been developed as disclosed in Japanese patent application laid-open No. 26383/1986.
When video signals in the NTSC system for example are indicated by the above-mentioned image display device, in the prior art, display elements of 480 scan lines or more corresponding to the effective picture plane of the NTSC system are installed and driven alternately in every other scan line, thereby producing a display similar to the interlace system of a so-called cathode ray tube.
In the above-mentioned image display device, however, since the distance between the display elements can not be made very small, when the display elements of 480 scan lines or more are installed as above described, the whole device becomes significantly large.
Therefore it is being studied that the number of the display elements is made that of 240 scan lines corresponding to one field, and the display of so-called non-interlace system is performed.
In this case, in the most simple method, common display elements are driven by video signals per each field. In this method, however, the display becomes similar to the case that so-called pairing is produced in a cathode ray tube, and the picture quality is significantly deteriorated, for example, so-called line crawling is produced in the edge portion of the
On the other hand, another method is in that in one field, the video signal is used as it is, and in the other field of the frame, upper and lower scan lines are added in a level ratio of 1/2, so that signals corresponding to scan lines of one field are formed and the common display elements are driven by these video signals. This can prevent the above-mentioned line crawling. In this method, however, since the processing of the video signal is different in one field and the other field, so-called flicker may be produced due to the level variation between them.
In the above-mentioned references, for example, a scan line conversion device is disclosed where 970 lines among the scan lines of high vision are converted in the ratio of 1/2 to form 485 scan lines of the NTSC system. That is, FIG. 3 shows procedure of the conversion. FIG. 3A shows the original signal (high vision), and a scan line in one field is shown by solid line and a scan line in the other field is shown by broken line respectively.
In FIG. 3, a first scan line (1o) and second scan line (2o) in one field are added in a level ratio of 3/4 (first) and 1/4 (second) respectively, to thereby form a signal corresponding to a first scan line (1'o) in one field, as shown in FIG. 3B. In a similar manner, from a third scan line (3o) and a fourth scan line (4o), from a fifth scan line (5o) and a sixth scan line (6o) . . . signals of a second scan line (2'o), a third scan line (3'o) . . . in solid line are formed in sequence.
Also a first scan line (1e) and a second scan line (2e) in the other field (of the frame) are added in a level ratio of 1/4 (first) and 3/4 (second) respectively, to thereby form a signal corresponding to a first scan line (1'e) in the other field as shown by broken line in FIG. 3B. In a similar manner, from a third scan line (3e) and a fourth scan line (4e), from a fifth scan line (5e) and a sixth scan line (6e) . . . , a second scan line (2'e), a third scan line (3'e) . . . in broken line are formed in sequence.
Consequently in this device, from signals of one field and the other field in high vision, signals of one field and other field in the NTSC system are formed, respectively, to thereby display an image in the NTSC system in interlace fashion. However, if this device is applied to the case that video signals in the NTSC system are displayed by the 240 scan lines as above described, the video signals in the interlace system of 240.times.2 fields are converted into that in the interlace system of 120.times.2 fields. In the image in such an interlace system, since the apparent resolution is decreased to about 70% (240.times.70%=168) due to so-called kell factor, the picture quality is deteriorated significantly.